Heat pipes are closed vessels having a chamber therein. There is a heat input portion and a heat output portion of the heat pipe. Fluid in the chamber circulates and principally transfers heat by the heat of vaporization and condensation, coupled with mass transfer of vapor and liquid. The heat pipe utilizes evaporation and condensation of the fluid and achieves efficient heat transfer by mass transfer of the fluid. The heat pipe working fluid may be water, ammonia, methanol or other alcohols, or halogenated hydrocarbons, such as freon. The particular working fluid and the quantity of that working fluid which relates to the working pressure of the heat pipe are chosen in accordance with the range of temperatures expected to be encountered in operation of the heat pipe in accordance with material compatibility properties.
The working fluid in the chamber of the heat pipe is thus critical with respect to both quantity and quality of the fluid fill or "charge". To achieve the correct fluid fill or "charge", present heat pipes are provided during their manufacture with an externally protruding filling tube which is in communication with the chamber. After the physical manufacturing is completed, the heat pipe is processed by charging it with the correct fluid. First, the fill tube is connected to a vacuum source to evacuate the original materials from the heat pipe chamber and, thereafter, the proper amount of the selected working fluid is charged through this fill tube. After filling, the tube is closed by crimping and welding to maintain the closed integrity of the heat pipe chamber. This method of charging the heat pipe is time-consuming, is a process which must be critically performed in order to be successful, is permanent, is difficult to achieve repeatability, and cannot be used for a recessed fill port. Therefore, there is need for a method and apparatus for evacuating and filling heat pipes and similar closed vessels so that the evacuation, filling and sealing of the vessels are quickly and reliably accomplished.